Method for processing a natural gas stream



1959 K. G. MITCHELL ETAL 2,909,905

METHOD FOR PROCESSING A NATURAL GAS STREAM Filed June 5. 195'! 2Sheets-Sheet 1 Fie.

KENNETH G5- MITCHELL-1 ROBERT E. MCPHNN a LAWTON L, LAURENCE INVENTORSAttorney 1959 K. s. MITCHELL ETAL 2,909,905

METHOD FOR PROCESSING A NATURAL GAS STREAM Filed June 5, 1957 2Sheets-Sheet 2 KENNETH 6 MITCHELL,

ROBERT E. MQIVHNN w LAWTON L .L AUR ENGE.

INVENTORS Attorney United States Patent (9 F METHOD FOR PROCESSING ANATURAL GAS STREAIVI Kenneth G. Mitchell, Robert E. McMinn, and LawtonL. Laurence, Oklahoma City, Okla assignors to Black, Sivalls & Bryson,Inc., Kansas City, Mo., :1 corporation of Delaware Application June 5,1957, Serial No. 663,823 2 Claims. (Cl. 62-23) The present inventionrelates generally to "a method for processing a hydrocarbon fluid streamto recover the desirable liquefiable hydrocarbon components from thestream.

The processing of natural gas streams under pressure requires that thetemperature of the stream be reduced to an extent whereby the maximumamount of desirable liquefiable components of the stream are recoveredfrom the stream. Such processing requires substantial artificial coolingof the stream, especially when suflicient excess pressure is notavailable for expansion cooling. Therefore, the primary object of thepresent invention is to provide a method for processing such a fluidstream to obtain a maximum recovery of desirable liquefiable componentsof the fluid stream.

Anotherobject of the present invention is to provide a method ofprocessing a natural gas stream with artificial refrigeration in whichthe gas stream is used to absorb a substantial portion of the heatnecessary for the artificial refrigeration. A still further object ofthe present invention is to provide a more efiicient method ofprocessing a natural gas stream with artificial refrigeration to recoverthe desirable liquefiable hydrocarbons. Still another object of thepresent invention is to provide an improved method of processing anatural gas stream with an absorption type refrigeration.

.In accomplishing these and other objects of the present invention, wehave provided an improved process which may readily be understood byreference to the accompanying drawings wherein:

Fig. 1 is a flow diagram of a form of apparatus for practicing thepreferred method of the present invention.

Fig. 2 is a flow diagram of a modified form of the present invention.

Referring morein detail to the drawings:

A hydrocarbon fluid stream such as a natural gas well stream underpressure is conducted to the system illustrated in Fig. 1 throughinfluent duct 1. In order to better illustrate the advantages of thepresent invention, temperatures and pressures of a fluid stream will beassumed, it being understood that these assumptions are for the purposeof illustration rather than any definite limitation. For example, afluid stream having a pressure of eight hundred (800) pounds per squareinch and an influent temperature of 70 F. would benefit from the methodof the present invention as disclosed in Fig. 1.

The influent stream flowing through duct 1 is split whereby one portionof the stream is conducted to heat exchanger 2 and the other portion toheat exchanger 3 through ducts 4 and 5 respectively. The well streamfluids are cooled in both heat exchangers 2 and 3 and are dischargedtherefrom through ducts ,6 and 7. These two portions of the fluid streamare combined and conducted through duct 8, heat exchanger 9, duct intoseparator 11. The fluid stream is further cooled in heat exchanger 9 byartificial refrigeration as hereinafter more fully explained. Thus, itcan be seen that without the patented Oct. 27, 1959 ice advantage ofhaving sufiicient excess pressure to allow for expansion cooling of thefluid stream that the temperature of the fluid stream flowing throughduct 8 can approach F. or lower and the temperature of the fluid streamflowing through duct 10 in separator 11 may be 0 F. or lower, thepressure remaining substantially constant (800 pounds per square inch)throughout the entire system previously described.

Gas outlet duct 12 conducts gas separated from the fluid stream withinseparator 11 to heat exchanger 2 at a temperature of approximately 0 F.After providing this cooling of a portion of the influent fluid stream,the separated gas being discharged from heat exchanger 2 through duct 13will have a temperature of approximately 60 F. and still a pressure ofapproximately 800 pounds per square inch.

The liquids separated from the fluid stream are discharged throughliquid outlet duct 14 which connects into heat exchanger 3. Pressurereducing valve 15 is positioned in liquid outlet duct 14 near heatexchanger 3 to reduce the pressure of the separated liquids from 800pounds down to approximately pounds per square inch.- The liquids, aftercooling the portion of the influent fluid stream flowing through heatexchanger 3, are discharged through duct 16 having a temperature of 60F. It should be noted that the volume of flow through heat exchanger 2and heat exchanger 3 should be controlled to allow the greatestefliciency of cooling of the fluid stream.

Liquid ammonia at approximately 200 pounds per square inch pressure issupplied to heat exchanger 9 through duct 17 and pressure reducing valve18. The ammonia vapors, after cooling the fluid stream within heatexchanger 9, are discharged through vapor duct 19 into absorber 20. Theammonia vapors delivered to absorber 20 are absorbed by weak solutionsof ammonia in water and are discharged through pump 21 and duct 22 as aliquid having a greater concentration of ammonia in the solution.Warming of the solution flowing through duct 22 takes place in heatexchanger 23 prior to the discharge of the solution into generator 24.Heater 25 heats the solution gathering in the lower portion of generator24 in order to drive off the ammonia vapors. These vapors rise throughgenerator 24, are discharged out through duct 26 and are condensed incondenser 27. The condensed liquid flows into duct 17 thereby completingthe refrigeration cycle. The vapors rising in generator 24 are cooled bycooling coils 28 in the upper portion of generator 24. This coolingprovides suflicient cooling to reflux generator 24. If desired, coils 28may be eliminated and a portion of the liquids condensed in condenser 27may be delivered to the upper portion of generator 24 to providerefluxing. Weak solutions are drawn from the lower portion of generator.24 and conducted through ducts 29 and heat exchanger 23 wherein'thesolution to be dumped into generator 24 is warmed and the weak solutionis discharged into absorber 20 preferably in the form of a spray inorder to absorb the ammonia vapors being discharged therein through duct19. Since the ammonia vapors may be driven out of solution by heat, ithas often been found necessary to cool "absorber 20 with cooling coils30.

Pump 31 provides circulation of a heat exchange medium such as waterthrough the cooling system for the absorption refrigeration systemhereinbefore described. This heat exchange medium is pumped by pump 31through duct 32 and divided into two streams flowing through ducts 33and 34 into heat exchangers 35 and 36. The cooled heat exchange mediumflows out of heat exchangers 35 and 36 and is conducted through header37 and duct 38 to cooling coils 30 within absorber" 20. The heatexchange medium being discharged from cooling coils 30 is conductedthrough duct 39 to return header 40 which connects into pump 31. Duct 41connects into header 37 and delivers heat exchange medium to condenser27 to cool and'condense the ammoniavapors passing through condenser 27.The heat exchange medium leaving condenser '27'is conducted through duct42 back to return header 40. Duct 43' connects into header 37' andconducts cooling medium to. cooling coils 28 within generator 24. Duct44 conducts the discharge of heat exchange medium from cooling coils 28to return header 40.

When properly operated and all heat exchangers being properly sized, itmay be assumed that the'heat exchange medium temperature prior to anyheat exchange. willbe 65 F. and that its temperature subsequent to heatexchange will be approximately 105 F. Under these circumstances the heatexchange within heat exchangers 35' and 36 between the heat exchangemedium and the two phases, gas at 800 pounds per. square inchand 60 F.and liquid atl pounds per. square inch and 60 R, will provide sufiicientcooling to reduce the temperature of the heat exchange medium from 105F. down to the assumed initial temperature of 65 F. The gas' flowingfrom heat exchanger 35 through duct 45 will then be at approximately 100F. and 800 pounds per square inch. The liquid which is dischargedthrough duct 46 from heat exchanger 36 will be at a temperature'ofapproximately 100 F. and 100 pounds per square inch.

Referring to the flow diagram illustrated in Fig. 2, the influent streamis conducted into the system through'duct 47 and to heat exchangers 49and 52 through ducts 48 and 51. As in the system shown in Fig. 1, thestream is split, with one portion flowing through the gas cooler 49 andbeing discharged therefrom through pipe 50 and into duct 55. The otherportion of the stream flows through duct 51, heat exchangers 52 and 53'and is conducted through duct 54 to combine with the streamflowingthrough duct 50 into duct 55. through artificial cooler 56 and duct 57into separator 58. The gas from separator 58 is conducted through duct59 to heat exchanger 49 wherein the cold gas is'utilized to cool aportion of the influent fluid stream. -Thegas leaving heat exchanger 49is conducted through duct 60 to the refrigeration equipment ashereinafter more fully described. The liquid is discharged fromseparator 58 through duct 61 to heat exchanger 53 wherein it cools theportion of the fluid stream flowing through heat exchanger -3. Duct 62conducts the liquids from heat exchanger 53 into second stage separator63. Separator 63 separates the gases which are vaporized from the liquiddue to the heating of the-liquids within heat exchanger 53. These gasesare discharged through duct 64 and are combined with the gas streamflowing through duct 60. The liquids are discharged from separator 63through duct 65, pressure reducing valve 66 and into heat exchan er 52.These liquids, after cooling the portion of the well stream flowingthrough heat exchanger 52 The total stream flows are dischargedtherefrom through duct 67 and are delivered to the refrigeration systemas hereinafter more fully described.

Liquid refrigerant is delivered to heat exchanger 56 through duct 68 andpressure reducing valve 69; .The vapors of the refrigerant which aredischarged from heat exchanger 56 are conducted through duct70into'absorber 71 wherein these vapors are absorbed intoa water solution.The water solution is discharged from absorber 71 through duct 72, pump73, duct 74, heat exchanger 75, duct 76 and into generator 77.

Heater 78 provides the necessary heating of the liquids collectingwithin the lower portion of generator 77. Liquids are discharged throughduct 79 and are passed in heat exchange relation with the liquid flowingthrough heat exchanger 75 from absorber 71. The liquids from generator77, being cooled and having warmed the" liquid solution which is to bedumped into generator 77, are conducted through duct 80 and sprayed intoabsorber '71 in such a manner as will best enable the liquids to pick upthe vapors flowing into absorber 71 through duct 70. Duct 81 connectsinto the liquid discharge duct 72 and conducts a portion of the liquidsfrom absorber 71 through pump 82, heat exchanger 83, duct 84 and intoduct 80 which discharges the liquid from the lower portion of generator77 and from heat exchanger 75 into absorber 71.

The gas being discharged from the system is conducted through duct 60into heat exchanger 83 wherein the gas absorbs a portion of the heatcontained in the liquids within absorber 71. The gas passes from heatexchanger 83 and is delivered through duct 85 to any suitable pipelineor gas transmission system. It is believed that the cooling of theliquids from absorber 71 will be sufficient so that internal coolingcoils will not beneeded- If sufficient heat is not absorbed by the gasstream in heat exchanger 83, then additional cooling may be used.without departing from the spirit of the present invention. This may bein the form of flowing a cooling medium through heat exchange coilswithin absorber 71 and allowing the cooling medium to be air cooled.

The vapors boiled out of the liquid in generator 77 are conducted outthrough duct 86 into condenser 87 and are delivered through cooler 88 toduct 68 and pressure reducing valve 69 wherein the liquid condensed incondenser 87 is again used to provide cooling for the fluid stream heatexchange in heat exchanger 56. The liquids which are dischargedfrom'heat exchanger 52 through duct 67 are connected to cooling coil 89within generator 77 and to condenser 87. This cools the upper portion ofgenerator 77 to provide a reflux of condensed vapors. Reflux liquidcould be provided from condenser 87, thus eliminating the necessity ofcooling coil 89 in generator 77. The liquids are then discharged throughduct 90 to suitable liquid storage facilities or to processingfacilities for stabilization or fractionation. The liquid providessuflicient cooling of the refrigerant vapors in cooling coils 89 andcondenser '87 and eliminates the necessity for a substantial amount ofadditional cooling in the refrigeration system. The extent to which theliquids can be used for cooling must be thoroughly understood and theamount of heat absorbed by these liquids should. be definitely limitedso as to comply with the temperature and pressure requirements forstorage or the required pressure and temperatures of the liquid for anyprocessing equipment to which the liquids are to be delivered-Therefore, from the foregoing description it can be seen that we haveprovided a novel system for processing a fluid stream whereby thecomponents of such stream are cooled, separated, used for initiallyprecooling the fluid stream and subsequently for absorbing heat from theartificial refrigeration system which also is used to cool the influentstream. We have provided a system which takes advantage of the heatwhich may be absorbed by the separated components of the fluid stream.For example, it is often a tremendous heat saving to be able to heat thegas stream going to a pipeline to a temperature of approximately F. Thisisadvantageous if the stream is to be transported through a pipelinesince it warms the gas to a temperature substantially above its dewpoint, thus further protecting the pipeline against condensation.Utilizing these streams to absorb heat will result in a large savingboth in original equipment needed (such as water cooling towers) and inreduced operating costs.

D What we claim and desireto secure by Letters Patent 1s:

1. The method of processing a hydrocarbon fluid stream comprising,dividing said fluid stream. into a first stream and a second. stream,precooling saidfirst stream and said second stream, recombining saidfirst.

separating the condensed liquids from said recombined stream, flowingsaid separated liquids into heat exchange relation with said secondstream to precool said second stream, flowing the liquid-free fluidstream into heat exchange relation with said first stream to precoolsaid first stream, flowing said separated liquids into heat exchangerelation with refrigerant vapor to condense said refrigerant vapor,expanding said condensed refrigerant, flowing said expanded refrigerantinto heat exchange relation with said fluid stream to provide saidcooling of said fluid stream, absorbing said expanded refrigerant withan absorbent liquid, heating said absorbent liquid to vaporize saidabsorbed refrigerant, flowing said refrigerant vapors into heat exchangerelation with said separated liquids to condense said refrigerantvapors, flowing said liquid-free fluid stream into heat exchangerelation with said absorbent liquid to cool said liquid.

2. The method of processing a hydrocarbon fluid stream comprising,dividing said fluid stream into a first stream and a second stream,precooling said first stream and said second stream, recombining saidfirst and said second streams, cooling said recombined stream,separating the condensed liquids from said recombined stream, flowingsaid separated liquids into heat exchange relation with said secondstream to precool said second stream, flowing the liquid-free fluidstream into heat exchange relation with said first stream to precoolsaid first stream,

separating the gases released from said separated liquids by the heatexchange with said second stream, combining said separated gases intosaid liquid-free fluid stream, flowing said gas-free liquid stream intoheat exchange with refrigerant vapor to condense said refrigerant vapor,expanding said condensed refrigerant, flowing said expanded refrigerantinto heat exchange relation with said fluid stream to provide saidcooling of said fluid stream, absorbing said expanded refrigerant withan absorbent liquid, heating said absorbent liquid to vaporize saidabsorbed refrigerant, flowing said refrigerant vapors into heat exchangerelation with said gas-free liquid stream to condense said refrigerantvapors, flowing said liquid-free fluid stream into heat exchangerelation with said absorbent liquid to cool said liquid.

References Cited in the file of this patent UNITED STATES PATENTS2,265,527 Hill Dec. 9, 1941 2,265,558 Ward et al. Dec. 9, 1941 2,336,097Hutchinson Dec. 7, 1943 2,601,599 Deming June 24, 1952 2,704,274 AllisonMar. 15, 1955 2,726,519 Squier Dec. 13, 1955 2,742,407 Irvine Apr. 17,1956 2,826,049 Gilmore Mar. 11, 1958

1. THE METHOD OF PROCESSING A HYDROCARBON FLUID STREAM COMPRISING,DIVIDING SAID FLUID STREAM INTO A FIRST STREAM AND A SECOND STREAM,PRECOOLING SAID FIRST STREAM AND SAID SECOND STREAM, RECOMBINING SAIDFIRST AND SAID SECOND STREAM, COOLING SAID RECOMBINED STREAM, SEPARATINGTHE CONDENSED LIQUIDS FROM SAID RECOMBINED STREAM, FLOWING SAIDSEPARATED LIQUIDS INTO HEAT EXCHANGE REALTION WITH SAID SECOND STREAMTOI PRECOOL SAID SECOND STREAM, FLOWING THE LIQUID-FREE FLUID STREAMINTO LEAT EXCHANGE RELATIION WITH SAID FIRST STREAM TO PRECOOL SAIDFIRST STREAM, FLOWING SAID SEPARATED LIQUIDS INTO HEAT EXCHANGE RELATIONWITH REFRIGERANT VAPOR TO CONDENSE SAID REFRIGERANT VAPOR, EXPANDINGSAID CONDENSED REFRIGERANT, FLOWING SAID EXPANDED REFRIGERANT INTO HEATEXCHANGE RELATION WITH SAID FLUID STREAM TO PROVIDE SAID COOLING OF SAIDFLUID STREAM, ABSORBING SAID EXPANDED REFRIGERANT WITH AN ABSORBENTLIQUID, HEATING SAID ABSORBENT LIQUID TO VAPORIZE SAID ABSORBEDREFRIGERANT, FLOWING SAID REFRIGERANT VAPORS INTO HEAT EXCHANGE RELATIONWITH SAID SEPARATED LIQUIDS TO CONDENSE SAID REFRIGERANT VAPORS, FLOWINGSAID LIQUID-FREE FLUID STREAM INTO HEAT EXCHANGE RELATION WITH SAIDABSORBENT LIQUID TO COOL SAID LIQUID.